Dear Sir,
I use the TSH4130 FDA to provide the ADC input. The ADC works in external reference mode. The Vcm (3.1V typ.) is generated by the ADC and supplied to the FDA. The Vocm FDA input absorbs few hundred of uA (confirmed both in simulation and measure) but, since the FDA Vcm output is buffered by a 2 k resistor, the Vocm voltage of the differential signal is about 2.8V. But inside the input "Analog Input Circuit" (data-sheet @ pag. 28) of the ADC the Vocm appears applied to the common node of the differential signal.
I wonder if the applied internal voltage (reported in "Analog input circuit") is downstream or upstream of the buffer resistor. Because if is upstream of the buffer resistance, a difference voltage of about 300 mV will be present between Vcm_signal and Vcm. On the contrary, a voltage of about 2.8V will be the Vocm of the system.
Which is the case? Depending on it, does the system works well?
Thank you
Davide